In the case of controlling an AC rotating machine to drive a mechanical device, in order to drive the AC rotating machine connected to the mechanical device with a desired response, it is necessary to identify a machine constant of the mechanical device to which the AC rotating machine is connected. However, the actual mechanical device has a complicated mechanism, and it is often difficult to grasp the precise machine constant. In order to solve such a problem, there is a conventional method of estimating the moment of inertia which is the machine constant of the mechanical device.
For example, in the method described in Non-Patent Document 1, current of the AC rotating machine is detected to calculate torque, and the rotation speed of the AC rotating machine is detected using a speed sensor and a position sensor. An acceleration component is calculated from the rotation speed, and on the basis of the equation of motion for the AC rotating machine, the moment of inertia is calculated using a statistical method. In this case, since the speed sensor and the position sensor are used, there is a disadvantage in failure resistance and maintenance.
Therefore, in order to estimate the moment of inertia of the mechanical device without using these sensors, a vector control inverter device is proposed as a conventional control device for AC rotating machine.
The vector control inverter device gives a certain torque axis (q-axis) current command to the AC rotating machine which is rotated at a constant speed by angular speed control, thereby causing minute change. Then, the torque change amount is calculated from the detected current, and an acceleration component is extracted from estimated speeds of the AC rotating machine before and after the torque axis current command is changed, thereby calculating the moment of inertia (see, for example, Patent Document 1).
Non-Patent Document 2 discloses a design method for a speed estimation gain and a feedback gain for an adaptive observer which is configured on rotational two axes in position sensorless control for an electric motor.